It’s always concerning when your car’s AC begins to make unusual noises. There are so many pieces under the hood of a vehicle that it can be daunting, and you may not know where to begin.
If your car AC is making noise, this can be due to loose screws, a bad compressor clutch, refrigerant problems, or a bad drive belt. Identifying and addressing the issue as soon as possible prevents long-term damage to the car.
This article will look at the most common causes of a loud car AC and discuss how to get to the bottom of what is happening in your car. Although noise from your AC could indicate any problem under the hood, it is always best to start at the source and work outwards.
1. Loose Screws
The screws that hold the car’s AC components together can loosen over time and cause a rattling sound. If you hear a rattling sound whenever the AC turns on, checking your screws is the best first step.
The easiest way to fix loose screws is to open up your hood while the AC is running and visually inspect the unit to see what is shaking. Make sure to check the screws on your air filters, which are a common problem area.
After you have tightened your screws, adding a liquid thread lock can help prevent the problem in the future.
2. Compressor Clutch
Inside the compressor, there is a piece called the compressor clutch, which powers the AC system by engaging a pulley. As soon as you turn on the AC, it begins pulling power from the engine to run.
The compressor clutch has three parts: an armature, a pulley, and a coil. If the pulley stalls when you turn on the AC, it can create a screeching noise and receive damage.
If you suspect something may be wrong with your compressor clutch, stop using your car’s AC immediately to prevent serious damage to your compressor, which happens to be the most expensive part to replace. Taking your car to a local auto repair shop is the best option.
3. Refrigerant or Oil Leak
Your car’s AC has two fluids inside of it: refrigerant and compressor oil. Because the AC is a closed system, it maintains the same amount of fluid without losing any to evaporation. When this seal is broken and fluid leaks out, the AC may begin to make a clicking sound due to a lack of liquid.
In addition to a clicking sound, weak airflow or warm air in the car can also indicate that you may have a leak on your hands.
To confirm a leak, you should inspect the AC system and hoses for an oily substance, which can look slightly green. If you don’t see anything, you can use UV dye. Some refrigerant comes with dye already in it, though you may need to purchase some to add separately. Once you inject the dye and run the AC for a bit, the leak will glow under a UV light.
If the leak is small, a short-term solution is to use a product called AC Stop Leak, which comes in many different brands. With the AC running, attach the can to the service port near the compressor.
Then follow the instructions to empty the can into your system. Stop leak is a short-term solution, and it is not a replacement for large amounts of oil that may have come out. Ultimately, you will need to contact a local auto repair shop to find a long-term solution.
4. Too Much Refrigerant
An overcharged AC (unit with too much refrigerant) can cause a buzzing noise in your vehicle. If there is too much refrigerant, the evaporator will not have enough room for the liquid to become gas. That means that your AC will be sending liquid into the compressor instead of gas, which can cause real damage to your system.
You will need to take your car to a professional to have them measure the pressure in your AC and drain any excess refrigerant. Trying to drain refrigerant by yourself can be dangerous. Firstly, many gauges can be inaccurate, and relying on them can worsen the problem. Secondly, refrigerants are considered greenhouse gasses, and there are specific protocols for disposal.
5. Failing Drive Belt
The drive belt connects your car’s engine to many other systems in your car and contributes to powering the AC system. While you can operate a vehicle without an AC system, it will not go anywhere if the drive belt is not working.
If you hear a squealing sound through your AC vents but find no problem with the AC itself, it’s time to look at the drive belt. Your belt may need to be realigned, have the tension adjusted, or be replaced altogether. A professional can help you determine the best course of action.
You must never use lubricant on your drive belt, even if it claims to be effective for belts. Lubricants are a temporary fix at best and can ultimately cause further damage to the belt.
You should follow the instructions in your car’s owner’s manual on how often you need to get your drive belt replaced.
Diagnosing the Problem With Your Car AC
While it’s relatively easy to tell whether or not something is working incorrectly in your car, it can be a lot trickier to diagnose the true root cause of the issue.
This section will tell you everything you need to know about how the AC system works, so you can gain a better understanding of your car’s functionality and get down to the foundation of the problem.
How a Car AC Works
Before you begin to address potential issues with your AC system, it’s important to understand how your car’s AC works. Having a general understanding of the system and its functions can help you think critically about what could be causing problems in your vehicle.
The AC in your car is a closed system that pumps refrigerant. The AC uses pressure to heat and cool the air as the refrigerant travels around.
Here’s a basic rundown of the process:
- The compressor takes the refrigerant, which is a gas at this point, and squeezes it to increase the temperature and pressure.
- Then it moves to the condenser, which uses a fan to cool the refrigerant down, making it a liquid.
- The liquid refrigerant then goes through the receiver/dryer, where it is filtered to remove contaminants and water.
- Next, the expansion valve creates room for the pressure to drop, which causes the temperature to drop.
- From there, the evaporator turns the refrigerant from a liquid to a gas. This change causes the refrigerant to absorb the heat around it, making the surrounding air cold. A fan then carries the cool air into the interior of the car.
As you cool off, the refrigerant is already on its way back to the compressor to start all over again.
This YouTube video does an excellent job of explaining how your car’s AC works:
How to Narrow Down Car AC Problems
It is always best to try and prevent damage to your car’s AC through inspections and following the manufacturer’s recommendations, but issues will still happen from time to time. Addressing a noisy car AC early on will save you time, money, and stress in the future.
One way to narrow down your car’s issue is by the type of noise you are hearing.
Here are some common AC noises and what they might mean:
- A rattling sound can mean loose screws.
- If you hear screeching, start with the compressor clutch.
- Clicking is associated with refrigerant or oil leaks.
- Buzzing can be a sign of too much refrigerant.
- Squealing points to a failing drive belt.
If you are unable to find the source of the noise or are uncomfortable working under the hood, it is worth giving your local auto repair shop a call for a complete diagnostic assessment.
Another Possible Source of Noise
A strange noise coming from your car’s AC does not always indicate a problem with the AC itself. Many systems under the hood, including the engine and belts, can produce a noise that sounds like it is coming out of your AC vents.
If you keep your AC running all of the time, turn it completely off for a few minutes. If the noise still comes through your AC vents, you may be dealing with a failing drive belt as opposed to an issue with the AC.
Preventing Car AC Malfunction
The best way to keep your AC in working order is to drive your car often. Most problems with car ACs occur when the system has not been in use for two or more weeks.
Although it may be tempting to measure the pressure in the AC system from time to time, it is best not to fiddle with the AC if it is working. Your system should never require more refrigerant to the system when it is working properly. You may need to replace excessive refrigerant lost through a leak, and even then, you need to be careful of overfilling. The AC is a closed system, so it will not lose any refrigerant when operating correctly. Checking the pressure levels is not necessary for routine maintenance.
It is also essential to have your car inspected regularly to address any problems before they become a more significant issue. A good rule of thumb is to get an inspection every 3-6 months, or along with every oil change, whichever comes first.
Final Thoughts
It can be daunting to hear a strange sound coming from the inside of your car, especially the AC system. However, getting to the root cause of the issue and addressing the problem early can help promote the functionality and overall longevity of your vehicle.
Hopefully, this article has helped you achieve a better understanding of your AC, so you can tackle malfunctions before they become too large of a problem – and feel a lot safer while out on the road.
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